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Research Papers

Endwall Contouring Using Continuous Diffusion: A New Method and its Application to a Three-Stage High Pressure Turbine

[+] Author and Article Information
M. T. Schobeiri

e-mail: tschobeiri@tamu.edu

K. Lu

Turbomachinery Performance and Flow
Research Laboratory,
Texas A&M University,
College Station, TX 77845

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received June 27, 2012; final manuscript received September 24, 2012; published online September 20, 2013. Editor: David Wisler.

J. Turbomach 136(1), 011006 (Sep 20, 2013) (10 pages) Paper No: TURBO-12-1081; doi: 10.1115/1.4023970 History: Received June 27, 2012; Revised September 24, 2012

Blades of high pressure turbines have a relatively small aspect ratio that produces major secondary flow regions close to the hub and tip. The secondary flows caused by a system of hub and tip vortices induce drag forces resulting in an increase of secondary flow losses, and thus, a reduction of stage efficiency. Given the high level of technological maturity and the current state of turbine aerodynamic efficiency, major efficiency improvement, if any, can be achieved only by significant R&D effort. In contrast, a moderate increase in aerodynamic efficiency is attainable by reducing the effect of parasitic vortices such as those mentioned above. Introducing an appropriate nonaxisymmetric endwall contouring reduces the secondary flow effect caused by the pressure difference between pressure and suction surfaces. Likewise, attaching leading edge fillets reduces the strength of horseshoe vortices. While an appropriate endwall contouring design requires special care, the design of the leading edge fillet is straightforward. In this paper, we present a physics based method which enables researchers and engineers to design endwall contours for any arbitrary blade type regardless of the blade loading, degree of reaction, stage load and flow coefficients. A thorough step-by-step design instruction is followed by its application to the second rotor row of the three-stage research turbine of the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. Comprehensive numerical calculations of the flow field, including the secondary flow, show the positive impact of an appropriately designed endwall contouring on the efficiency. The results also show how an inappropriately designed contour can be detrimental to turbine efficiency.

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Figures

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Fig. 1

(top) Details of the new rotor; (bottom) the three-stage rotor

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Fig. 2

(a) Row-by-row configuration; (b) CFD mesh

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Fig. 3

Contouring using the conventional method

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Fig. 4

Contour variation: (a) partial positive contouring; (b) extended partial positive contouring; (c) partial positive, negative contouring; (d) extended partial positive negative contouring; (e) full passage contouring. The maximum positive height for all cases is 6 mm, and the minimum negative height is −3 mm.

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Fig. 5

Efficiency chart of numerically investigated cases

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Fig. 6

Distribution of Zweifel-coefficient as a function of inlet flow angle α1 with α2 = 18 deg and the spacing/chord ratio s/s as a parameter top (a), angle definition and different blade loading bottom (b)

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Fig. 7

Explaining the continuous diffusion process for designing physics based endwall contouring

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Fig. 9

Noncontoured (top), new contouring method (bottom)

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Fig. 10

Streamlines for reference case (top) and new contouring (bottom)

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Fig. 11

Pressure distribution directly on the hub, a target pressure is set the diffusion channel constructed that leads to endwall contouring

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Fig. 12

Pressure distributions on the hub

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Fig. 13

Pressure distributions above the hub

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Fig. 14

Contour plots of pressure distributions: (a) reference case, (b) extended partial positive, negative, (c) new contouring

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Fig. 15

Efficiency chart of all investigated wall contours

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Fig. 16

Total pressure loss coefficients for reference case, new contouring and extended partial positive, negative

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Fig. 17

Vorticity distribution in the passage

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